docs: def setTxPower(self, tx_power, peername=None):
          """Set the transmit power on one or all readers
  
          If peername is None, set the transmit power for all readers.
          Otherwise, set it for that specific reader.
          """
          if peername:
              protocols = [p for p in self.protocols
                           if p.peername[0] == peername]
          else:
              protocols = self.protocols
          for proto in protocols:
              proto.setTxPower(tx_power)